It is desirable in the study of aerosols to generate dust aerosols from a substance initially in powder form. The powder should be dispersed into the carrier gas stream and all powder particles should appear in the gas stream as single particles rather than agglomerates of two or more particles. The concentration of particles in the gas stream should be constant with respect to time so that a steady dust stream can be obtained. Dust generators can be used to generate airborne dust from pulverized coal and other mineral and non-mineral substances for testing dust measuring and collecting equipment. Alternatively, the dust generator can be used in animal-exposure experiments where the toxicity of the inhaled dust particles can be assessed.
A number of instruments have been used to generate dust aerosols. Several dust generators have been reported in literature. Wright in the Journal of Scientific Instruments, 27:1, January, 1950, p. 12, discloses a dust generator wherein the particles are scraped from a rotating cylinder which has been packed with particles. The particles are picked up by a scraper and are made airborne by a flowing air stream passing through the scraper inlet. The particles moving with the air pass through a nozzle and impact on a plate to break up the agglomerates. This type of dust generator has the disadvantage of not providing a steady dust output since the column of powder must be packed to the same uniform density in order to achieve a steady output. Since uniform loading of the cylinder is difficult to obtain, the dust will appear in puffs rather than a steady stream. Also, the powder is not always steadily dispersed and the particles do not always appear as single individual particles.
Another form of the dust generator uses a groove in a rotating circular disc. The powder is packed into the groove and subsequently picked up by a jet of air as the groove rotates with respect to an air nozzle.
A dispersion-type generator described by Willeke et al in Aerosol Science, Volume 5, 1974, pages 449-455, uses a fluidized bed to disperse the powder particles. The powder particles are picked up by a gas stream flowing up through the fluidized bed. The powder to be dispersed is either premixed in the bed material or introduced into the fluidized bed. The dust dispersion is good but steady operation of the generator cannot be attained.